The internet port on the phone is connected to the network switch and the PC port is connected to the computer.

When the phone reboots, during the initializing period, the phone passes UNTAGGED packets to the PC port, therefore, as the network connection is temporality dropped on reboot, when it is re-established, the computer requests a new DHCP address and since the untagged VLAN 10 packets are being passed, an IP address in the range of 10.0.10.0/23 to the PCs instead of an IP address in the 172.16.10.0/23 range. Once the phone has restarted, the switch in the back of the phone operates as expected only allowing tagged VLAN 20 packets through. So renewing the IP address on the PC again, gives the correct IP address.

While its easy to fix, its quite annoying as every time any of our T42G or T46G are restarted, if there is a PC connected to the phone at that time, then it will get the wrong IP and therefore will not be able to connect to network services anymore.